Recently, as the existing energy resources, such as oil, coal and the like, became exhausted, alternative energy sources thereto have attracted attention. Among these alternative energy sources, solar cells are receiving particular attention because they are resourceful and do not cause environmental problems.
Solar cells include solar heat cells that generate steam necessary to rotate a turbine using solar heat and solar light cells that convert solar energy into electric energy using semiconductor properties. Solar cells are generally called solar light cells (hereinafter, referred to as ‘solar cells’).
Solar cells are largely classified into silicon solar cells, compound-semiconductor solar cells and tandem solar cells according to raw materials. Among these three kinds of solar cells, silicon solar cells are generally used in the solar cell market.
When solar light enters such a solar cell, electrons and holes are generated from a silicon semiconductor doped with impurities by a photovoltaic effect.
Such electrons and holes are respectively drawn toward an N-type semiconductor and a P-type semiconductor to move to an electrode connected with a lower portion of a substrate and an electrode connected with an upper portion of an emitter doping layer. When these electrodes are connected with each other by electric wires, electric current flows.
In this case, a conventional solar cell is manufactured by the following processes of: {circle around (1)} texturing; {circle around (2)} doping (forming a PN Junction); {circle around (3)} removing an oxide film (PSG: phosphor silicate glass); {circle around (4)} forming an anti-reflective film (ARC: anti-reflective coating); {circle around (5)} metallizing; and {circle around (6)} measuring edge isolation.
The texturing of a conventional solar cell (for example, a polycrystalline silicon solar cell) was mostly conducted using an acid solution (HNO3/HF composition). In addition, the texturing thereof was conducted by performing a wet SDR (sawing damage removal) process and then decreasing reflexibility using RIE (reactive ion etching) texturing and thus improving Isc (shot-circuit current: reverse (negative) current density occurring when light is applied in a state in which a circuit is shorted, that is, in a state in which external resistance does not exist.
In the case of RIE texturing, due to surface plasma damage, it is difficult to realize the degree of increase of efficiency attributable to the decrease of FF (fill factor) and Voc (open-circuit voltage) regardless of low reflexibility. In order to remove such plasma damage, a DRE (damage removal etching) process is carried out. That is, the conventional RIE texturing includes: {circle around (1)} a wet SDR process; {circle around (2)} an RIE process; {circle around (3)} a DRE process; {circle around (4)} a doping process; {circle around (5)} a PSG removal process; and {circle around (6)} other conventional solar cell processes.
In order to accomplish a conversion efficiency of about 15% using a polycrystalline substrate (that is, a wafer), surface texturing is not the most important factor. However, in order to manufacture a polycrystalline solar cell having a conversion efficiency of 16% or more, a texturing process capable of trapping light can be issued.
Such a conventional texturing process includes a wet etching process. A wet etching apparatus is provided in order to conduct such a wet etching process. Meanwhile, the RIE process is carried out by dry etching, whereas the DRE process is carried out by wet etching. Therefore, an additional wet etching apparatus is required in addition to RIE equipment.
Accordingly, owing to the above wet etching process and wet etching apparatus, there is a problem in that the damage rate of a substrate (that is, a wafer) increases.
Further, since an additional wet etching apparatus is required in order to perform the above wet etching process, there is a problem in that the installation and maintenance costs thereof increase.